Data Rep

Question 1

Absolute error

Answer 1

Postive difference between the actual value and the floating point value
[Actual number - floating number]

Question 2

Relative error

Answer 2

Absolute error divided by the actual value

Question 3

Disadvantage of majority voting

Answer 3

volume of data being transmitted is
increased with the repetition of bits

Question 4

Checksums

Answer 4

An algorithm is used to determine the value of a checksum based on the data being transmitted. There is no agreed algorithm for this and different systems will use their own solutions

Question 5

Check Digit

Answer 5

a type of checksum in which only a single digit is added to the transmitted data. This reduces the number of different algorithms that could be used to calculate the value of the check digit and so reduces the variety of errors that the method can detect.

Question 6

Digital to Analogue Conversion

Answer 6

When converting from digital to analogue, a device called a digital to analogue converter is used. The device reads a bit pattern representing an analogue signal
and outputs an analogue electrical current.

Question 7

Analogue to digital Conversion

Answer 7

Use an analogue to digital converter to convert the analogue signal to a digital bit pattern. The device works by taking a reading of an analogue signal at regular intervals and recording the value in a process called sampling. Samples are taken at a specific frequency, which determines the number of samples taken per second. Once the value of the analogue signal has been recorded, it can be stored digitally as a bit pattern.

Question 8

Nyquist Theorem

Answer 8

The Nyquist theorem states that the sampling rate of a digital audio file must be at least twice the frequency of the sound.

Question 9

Musical Instrument Digital Interface (MIDI)

Answer 9

Used with electronic musical instruments
which can be connected to computers, MIDI stores sound as a series of event messages,each of which represents an event in a piece of music. These can be thought of as a series of instructions which could be used to recreate a piece of music.

Question 10

Event messages a MIDI can store

Answer 10

-Duration of a note
-Instrument with which a note is played
-How loud a note is (Volume)

Question 11

Advantages of using a MIDI over a sampled recording of a piece of music

Answer 11

-Allows for easy manipulation without loss of quality
-Instruments can be changed
-Notes can be changed
-Durtation of notes can be altered
-Smaller in size

Question 12

Disadvantage of using a MIDI

Answer 12

Cant be used for storing speech
Often results in less realistic sound.

Question 13

Two methods of lossless compression

Answer 13

-RLE
-Dictionary encoding

Question 14

Run length encoding

Answer 14

Reduces the size of a file by removing repeated information and replacing it with one occurance of the repeated information followed by the number of times it is to be repeated.

Question 15

Dictionary encoding

Answer 15

A dictionary containing repeated data is appended to the file. This method results is a significant reduction in size, but don’t forget that the dictionary used to compress the data has to be present in the file in order for the image to be reproduced. This will increase the size of the file.

Question 16

Encryption

Answer 16

Process of scambling data so that it cannot be understood if intercepted in order to keep it secure during transmisson.

Question 17

Two types of caesar ciphers

Answer 17

-Shift ( All letters are shifted )
-Substitution ( Letters are randomly replaced )

Question 18

Disadvantage of caesar ciphers

Answer 18

Can be easily cracked

Question 19

Vernam cipher Method

Answer 19

1. Aligning the characters of the plaintext and the key
2. Converting each character to binary (using an information coding system)
3. Applying a logical XOR operation to the two bit patterns
4. Converting the result back to a character

Question 20

Vernam Cipher

Answer 20

Example of a one-time pad cipher. This means that each key should only ever be used once. Additionally, the Vernam cipher requires the key to be random and at least as long as the plaintext that is to be encrypted.